I have a few, actually...
Sceptile - Personally, the animé ruined this pokémon for me (especially with its weird dub voice). It was so overhyped amongst the fandom that it really got to be annoying, enough so that I can't stand Sceptile anymore. Honestly, it's not that great...Blaziken and Swampert are way better.
Mewtwo - I don't suppose this poke's achieved 'hate' status with me quite yet, but still...He's.way.overhyped. Everyone's just like 'OMG; his story iz liek SOOOO heartbreaking!!11! And his psychicnessesses is liek soooo cool!' Cut me a break. It's getting old.
There's a few more, but I don't feel like writing all that out right now, heh XD